Aluminum-alloy clad sheet

Abstract

There are provided an aluminum-alloy clad sheet and a clad sheet subjected to heating equivalent to brazing, which each have a high strength and an excellent erosion resistance and thus allow a reduction in thickness of a clad sheet subjected to heating equivalent to brazing such as an aluminum alloy radiator tube, and / or of a clad sheet such as an aluminum-alloy brazing sheet. An aluminum-alloy clad sheet or a clad sheet subjected to heating equivalent to brazing includes at least a core aluminum alloy sheet and an aluminum-alloy sacrificial anti-corrosive material cladded with each other, and is to be formed into a heat exchanger by brazing. The core aluminum alloy sheet includes a specified 3000 series composition. Furthermore, the strength and the erosion resistance of the core aluminum alloy sheet are improved through control of grain size distribution of precipitates having a size in a specified level in the core aluminum alloy sheet, or control of the average number density and the composition of dispersed particles therein.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an aluminum-alloy clad sheet having high strength and excellent erosion resistance, which is used for an aluminum-alloy heat exchanger (hereinafter, aluminum may be referred to as Al).[0003]2. Description of Related Art[0004]To reduce weight of a motor vehicle body, aluminum alloy materials are increasingly used for the components of the motor vehicle, such as a heat exchanger component, in place of typically used copper alloy materials. An anti-corrosive aluminum alloy material formed of a multilayered clad sheet (sometimes referred to as clad material) is used for the aluminum alloy materials for a heat exchanger component. The clad sheet includes at least a core aluminum alloy sheet and an aluminum-alloy sacrificial anti-corrosive material cladded with each other. The clad sheet is a raw material for a heat exchanger, which is formed into a heat exchanger by brazing. Hence, a simply c...

AI Technical Summary

Benefits of technology

[0088]The above-described Fe and Mg, and elements other than the listed elements are basically impurities. If, however, scrap materials of other aluminum alloys and / or low-purity Al metal are used as ingot materials in addition to high-purity Al metal from the viewpoint of recycling of aluminum alloy sheets, the unlisted elements may be mixed in. In addition, a reduction in each unlisted element to a detection limit or less inevitably increases cost, and therefore the unlisted elements may be contained in some degree. Hence, the unlisted elements may be contained within a range without disturbing the object and the advantageous effects of the invention. For example, the unlisted elements such as B may be contained up to 0.05%.

[0089]Si increases the strength of the core aluminum alloy sheet through formation of an intermetallic compound with Fe. Si is therefore contained at least 0.2% to secure the strength necessary for the clad sheet or the clad sheet subjected to heating equivalent to brazing. In contrast, an excessive content of Si causes formation of coarse compounds in the core, and thus causes a reduction in size of grains recrystallized during heating and annealing for brazing, which accelerates diffusion of a brazing material into the core during brazing, resulting in degradation in brazability of the clad sheet during heating for brazing. In addition, the excessive content of Si accelerates diffusion of Si during heating for brazing, leading to degradation in corrosion resistance of the clad sheet or the clad sheet subjected to heating equivalent to brazing. Si is therefore contained up to 1.5%. Consequently, the content of Si is within a range of 0.2 to 1.5%.(Cu: 0.05 to 1.2%)

[0090]Cu is dissolved in the aluminum alloy sheet, and improves the strength of the core aluminum alloy sheet. In addition, Cu causes the internal potential of the core to be noble, which improves the corrosion resistance of the core. Cu is therefore contained at least 0.05% to secure the strength necessary for the clad sheet or the clad sheet subjected to heating equivalent to brazing. In contrast, an excessive content of Cu accelerates precipitation of coarse Cu-based compounds in a crystal grain boundary during cooling after heating for brazing, which facilitates occurrence of intergranular corrosion, resulting in degradation in corrosion resistance. Cu is therefore contained up to 1.2%. Consequently, the content of Cu is within a range of 0.05 to 1.2%.(Mn: 0.5 to 1.8%)

[0091]Mn is an element that distributes the specified fine dispersed particles in the aluminum alloy sheet, and thus increases the strength of the core aluminum alloy sheet without reducing the corrosion resistance thereof. Moreover, Mn improves the vibration fatigue resistance and the fatigue failure resistance. Consequently, Mn is contained at least 0.5% to secure the strength necessary for the clad sheet or the clad sheet subjected to heating equivalent to brazing, and to improve the fatigue failure resistance.

[0092]In contrast, an excessive content of Mn increases the number density of coarse compounds, which rather decreases the number density of precipitates at each specified grain size to below the specified limit, resulting in degradation in vibration fatigue resistance and fatigue failure resistance. In addition, such an increase in number density of the coarse compounds reduces the formability of the aluminum-alloy clad sheet that may be thus cracked during working such as assembling into a component form. Mn is therefore contained up to 1.8%. Consequently, the content of Mn is within a range of 0.5 to 1.8%.(Ti: 0.03 to 0.3%)

[0093]Ti forms fine intermetallic compounds in the aluminum alloy sheet, and thus improves the corrosion resistance of the core aluminum alloy sheet. Ti is therefore contained at least 0.03% to secure the corrosion resistance necessary for the clad sheet or the clad sheet subjected to heating equivalent to brazing. In contrast, an excessive content of Ti increases the number density of coarse compounds, which degrades the formability of the aluminum-alloy clad sheet that may be thus cracked during working such as assembling into a component form. Ti is therefore contained up to 0.3%. Consequently, the content of Ti is within a range of 0.03 to 0.3%.(Fe: 1.0% or less (including 0%))

Problems solved by technology

For such a brazing sheet including the core having a small thickness of less than 0.17 mm, the above-described improvement ideas in the related art, such as control of the structure of the core aluminum alloy sheet, i.e., control of the average grain size and the number density of the fine precipitates, are in fact insufficient for achieving the demanded high strength and excellent erosion resistance.

Images